Fragments of yeast chromosomal DNA which are adjacent to natural crosslinks at the chromosome termini will be cloned into recombinant DNA vectors. The cloned fragments will be used to study their sequence arrangement, and to examine for homology with other chromosome termini. The replication of autonomously replicating yeast DNA fragments, introduced into yeast cells by transformation, will be examined. We will determine the gene requirments for replication, the time of replication in the cell cycle and (for multiple copy fragments) whether all copies are replicated each cell cycle. Whether these autonomously replicating elements are condensed into nucleosomal structures (chromatin) within the cell will also be examined. The general features of replication of the yeast dsRNA plasmids will be explored. Whether replication occurs in all phases of the cell cycle, whether duplication produces semiconserved molecules and how replication events are distributed among the multiple copy molecules will be studied.